Spirally-wound sheet heat exchangers have been proposed heretofore and generally comprise spiral coils of one or more sheets defining passages for the fluid between the turns thereof. The sheets are generally wound in pairs with one fluid passing between the sheets of the pair and the other fluid passing through the turns of each pair of sheets.
The fabrication of such heat exchangers must be held within very narrow structural tolerances and hence the manufacturing costs are high. The narrow tolerances are necessary to prevent mixing of the fluids and to ensure complete sealing of one fluid space from another fluid space.
The planar surfaces of the coil must therefore be substantially completely sealed and hence extremely flat sealing members and machining techniques must be used.
The versatility of the heat exchangers of this known type has been extremely limited and hence it is not always possible to select the flow direction of a particular fluid or to vary the number of fluids which may be subjected to mutual heat exchange. Not all fluids can be passed axially through the system and, in practice, the system has been restricted to the use of two fluids.
The cross-section of the flow passage is dependent upon the gap width between the pair of plates which are coiled and this depends, in turn, on the dimensions of the available sheet metal strip or band and could not be selected at will. Here again the versatility of the system is limited and it is necessary to operate with restricted throughflow capacity.